Common rail fuel systems typically employ multiple closed-nozzle fuel injectors to inject high pressure fuel into the combustion chambers of an engine. Each of these fuel injectors may include a nozzle assembly having a cylindrical bore with a nozzle supply passageway and a nozzle outlet. A needle check valve may be reciprocatingly disposed within the cylindrical bore and biased toward a closed position where the nozzle outlet is blocked. In response to a deliberate injection request, the needle check valve may be selectively moved to open the nozzle outlet, thereby allowing high pressure fuel to flow from the nozzle supply passageway into the combustion chamber.
During operation of the fuel injector, it is possible for a tip portion of the nozzle to fail, leaving the nozzle continuously open. In order to ensure that the high pressure fuel is not continuously pumped into the combustion chamber, the common rail fuel system may employ a leak limiter to limit fuel leakage through the nozzle. One such device is described in U.S. Pat. No. 6,109,542 (the '542 patent) issued to Morris et al. on Aug. 29, 2000. The '542 patent describes a nozzle cavity housing a nozzle valve element, and a limiter valve disposed upstream of the nozzle cavity. The limiter valve is moved to an open position just prior to an intended injection to selectively communicate high pressure fuel with the nozzle cavity. Between desired injections of fuel into an associated combustion chamber, the limiter valve member is moved to a closed position to block communication of the high pressure fuel with the nozzle cavity. When the limiter valve member is in the closed position, only the fuel already in the nozzle cavity may leak into the combustion chamber upon failure of the nozzle tip.
Although the limiter valve of the '542 patent may minimize the amount of fuel leakage from the nozzle cavity upon failure of the nozzle, it still allows all of the fuel already in the nozzle cavity to drain into the associated combustion chamber following each intended injection. This amount of fuel allowed to drain into the combustion chamber could still significantly affect engine performance, fuel consumption and emissions.
In addition, the limiter valve does not limit deliberate injections. In particular, even if the injector of the '542 patent has experienced nozzle failure, the limiter valve of the '542 patent will still move to the open position in response to a demand for injection. Under conditions of nozzle failure, even a deliberate injection could result in rough engine operation, poor fuel consumption, and increased emissions.
Further, the limiter valve of the '542 patent may be complex, expensive, and increase unreliability in the common rail system employing the limiter valve. In particular, because the limiter valve is additive and performs no function other than leak limiting, the overall cost of the common rail system employing the limiter valve must increase. The additional components of the limiter valve also add to the overall complexity and the number of potential failure modes of the common rail system.
The fuel injector of the present disclosure solves one or more of the problems set forth above.